...And if you have the original Walker trigger, as I did on my Rem 600's, the Timney replacements I installed are a safer design as there is no forward slipping piece to get fouling debris caught under. That piece was Walker's way of eliminating overtravel, but it proved to be able to cause firing on closing the bolt if debris got in under it. Clever idea, but just not executed in a way that would keep debris out. Mind you, it takes someone not being careful about the point of the muzzle when closing the bolt for there to be a serious resulting accident, but some folks will occasionally neglect to control that.
I'll add that a Walker trigger isn't the only thing that can cause that symptom. I also had a pre-Accutrigger on a Savage let a shot go on bolt closing because I had lightened the Rifle Basix replacement of the same mechanical type beyond what the simple direct-release design could handle, regardless of who made it (my fault), but at least I was on a hot line with the muzzle pointed at the berm when it occurred. I subsequently put on the trigger sold by Sharp Shooter Supply, and that handled it and allowed much better range of safe adjustment.